This sets the packetization period, how much fax data is carried per packet, for the primary high-speed data phase of a T.38 fax relay session on this DS0 group. A shorter packet period sends fax data more frequently in smaller chunks, which can improve resilience on lossy IP paths at the cost of more packet overhead, so this is a knob admins tune specifically for fax reliability over congested or jittery voice-over-IP links. An admin might reduce this value from a 30 ms default to 20 ms on a DS0 group serving fax machines across a jittery WAN link to reduce fax-page transmission errors.